This invention relates to liquid ring pumps, and more particularly to automatic control of the discharge ports in liquid ring pumps for enhancing the performance of the pump over an extended operating range.
The typical liquid ring pump has a rotor with generally radial blades eccentrically mounted for rotation in an annular housing. A quantity of pumping liquid (e.g., water) is maintained in the housing so that when the rotor rotates, the rotor blades engage the liquid and form it into an annular ring which circulates around the inner periphery of the housing with approximately the same angular velocity as the rotor. The rotor and its blades cooperate with the liquid ring to convey gas from an intake zone, where gas is admitted to the pump, to a compression zone, where the gas is discharged from the pump at a higher pressure than the intake pressure. As used herein and in the appended claims, the term "gas" means any gas, vapor, or gas-vapor mixture to be pumped.
The compression zone in a liquid ring pump has an appreciable pressure gradient circumferentially of the pump. The discharge port through which gas is discharged from the compression zone necessarily has appreciable circumferential extent. Accordingly, various portions of this discharge port typically sense different pressures along the pressure gradient of the compression zone. To achieve different compression ratios (compression ratio being defined herein to mean the ratio of discharge pressure to intake pressure, both pressures being measured external to the pump) it may therefore be necessary or desirable to effectively change the size and/or location of the discharge port, e.g., by selectively closing off certain segments or portions of the discharge port. For example, when a liquid ring pump being used as a vacuum pump is first started, it is typically operating at a low compression ratio and pumping a large quantity of gas. A discharge port extending circumferentially into the relatively low pressure portion of the compression zone is then desirable to prevent over-compression of the gas prior to discharge. Such over-compression undesirably increases the power required to operate the pump while the over-pressure condition exists. The pump may therefore have to be provided with a significantly larger motor than would otherwise be required in order to meet these relatively infrequent requirements. After the vacuum pump has been in operation for some time, the compression ratio typically increases and the quantity of gas pumped decreases. To extend the operating range of the pump (i.e., to increase the compression ratio attainable), it would be desirable to close off the portion of the discharge port communicating with the relatively low pressure portion of the compression zone. This prevents gas discharged from the pump via the relatively high pressure portion of the discharge port from re-entering the pump via the relatively low pressure portion of the discharge port.
Pumps with various types of mechanical check valves for selectively closing off portions of the discharge port have been proposed. Most such devices have such disadvantages as sticking, wear, or failure.
It is therefore an object of this invention to provide improved and simplified liquid ring pumps.
It is a more particular object of this invention to provide improved and simplified means for controlling the effective size and/or location of the discharge port in liquid ring pumps.